The Tweet: “Flies drink alcohol when they are sexually frustrated.”

Sexually frustrated flies will drink alcohol in order to feel rewarded. Male fruit flies that have been rejected by females will preferentially drink food containing 15% ethanol over food without alcohol, whereas sexually satisfied males will not, research published in Science in 2012 has concluded.

Males were held in tanks with virgin females, who were sexually receptive; mated females, who were not receptive to new males; and decapitated virgin females, who acted as a control. Males who were able to mate with virgin females ate only the alcohol-free food, rejected males chose the alcoholic food. If the males that were originally rejected were then allowed to mate and choose a food source again this time they went for the alcohol-free alternative. Interestingly, if males who were left frustrated were then reintroduced to a tank with a receptive virgin female they still refused to mate.

Researchers at the University of California, San Francisco identified neuropeptide F (NPF) as the molecule responsible for the behaviour. Levels of NPF were higher in males who successfully mated than those who were rejected. This molecule – similar to neuropeptide Y in humans – is thought to be involved in the neurological reward system. Flies who have achieved mating success will have higher levels of NPF, but unsuccessful males will seek the reward through other means. When NPF was artificially reduced in flies, the males still preferred to drink alcohol to achieve satisfaction.

Previous studies have shown that ethanol consumption is rewarding for fruit flies. For the sexually frustrated flies, alcohol was the next best way to achieve a NPF reward. This shows the complex relationship between neurological reward, alcohol and behaviour even in simple animals like fruit flies.

This work could lead to a better understanding of the human neurological reward system and its relationship with alcohol: “If neuropeptide Y turns out to be the transducer between the state of the psyche and the drive to abuse alcohol and drugs, one could develop therapies to inhibit neuropeptide Y receptors,” said Ulrike Heberlein, who led the research. Understanding how alcohol encourages a feeling of satisfaction and the role human neuropeptides have in this relationship might provide solutions for alcohol addiction.